Hydrogen reduction kinetics of different nickel and cobalt compounds
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
Tönning Hall (L4), Linnanmaa Campus
Topic of the dissertation
Hydrogen reduction kinetics of different nickel and cobalt compounds
Doctoral candidate
Master of Science Sonja Pöyhtäri
Faculty and unit
University of Oulu Graduate School, Faculty of Technology, Process Metallurgy Research Unit
Subject of study
Process Engineering
Opponent
Professor Merete Tangstad, Norwegian University of Science and Technology
Second opponent
Doctor Michael Zarl, K1-MET, Austria
Custos
Docent Eetu-Pekka Heikkinen, University of Oulu
From compounds to metals with hydrogen: Tracing the reduction of nickel and cobalt compounds
Hydrogen reduction is a promising low-carbon method for producing pure metals. This doctoral dissertation explores how various powdered nickel and cobalt compounds transform into metals in a hydrogen atmosphere, investigating the rates at which the reactions occur, how the reduction progresses at different temperatures, and which reaction mechanisms control the process. Previous research in the field has focused on the reduction of nickel and cobalt oxides. However, carbonates and hydroxides can also be used as starting materials for metal production, and their behavior during hydrogen reduction is less well understood.
Mass-loss data obtained from thermogravimetric experiments were analyzed using various mathematical methods, and the reaction mechanisms of cobalt powders were investigated in detail through interruption experiments conducted in a hydrogen furnace, which allowed for microscopic examination of intermediate products and the study of crystal structure development. The results confirmed that increasing temperature accelerates the reduction process and demonstrated that multistep reduction reactions cannot always be described unambiguously using a single mathematical reaction model. The activation energy calculated for the reduction of each starting material showed that hydroxides and carbonates require less energy to initiate the reaction compared to oxides. The studies demonstrated how the starting material significantly influences the reduction mechanisms. The reduction of cobalt hydroxides proceeded via nucleation, meaning that the new structure formed through the formation and growth of small nuclei. The reduction of cobalt carbonate, on the other hand, began at the particle surface and proceeded toward the particle core.
The dissertation demonstrates how the choice of starting material affects the reduction process and how it can be used to influence the final product. The research provides additional information on the hydrogen reduction of nickel and cobalt compounds, which can be utilized in the design of industrial processes.
Mass-loss data obtained from thermogravimetric experiments were analyzed using various mathematical methods, and the reaction mechanisms of cobalt powders were investigated in detail through interruption experiments conducted in a hydrogen furnace, which allowed for microscopic examination of intermediate products and the study of crystal structure development. The results confirmed that increasing temperature accelerates the reduction process and demonstrated that multistep reduction reactions cannot always be described unambiguously using a single mathematical reaction model. The activation energy calculated for the reduction of each starting material showed that hydroxides and carbonates require less energy to initiate the reaction compared to oxides. The studies demonstrated how the starting material significantly influences the reduction mechanisms. The reduction of cobalt hydroxides proceeded via nucleation, meaning that the new structure formed through the formation and growth of small nuclei. The reduction of cobalt carbonate, on the other hand, began at the particle surface and proceeded toward the particle core.
The dissertation demonstrates how the choice of starting material affects the reduction process and how it can be used to influence the final product. The research provides additional information on the hydrogen reduction of nickel and cobalt compounds, which can be utilized in the design of industrial processes.
Created 13.10.2026 | Updated 14.10.2026